That's not the same thing, though. They're not just talking about the fact that some items are more common than others, or even the correlation between power an

That's not the same thing, though. They're not just talking about the fact that some items are more common than others, or even the correlation between power and rarity. What Diablo did (that M:tG didn't) was that the same weapon could have multiple rarities, with the rarer versions being more powerful. Each card in M:tG has only a single rarity, and the foil version is just a cosmetic difference with no gameplay effect. An Uncommon (or equivalent) in Diablo is not a sui generis item, it is a common with upgraded stats. A Rare is the same thing with magic effects added.